Metal quenching medium



3,220,893 METAL QUENCHING MEDIUM Robert Ross Blackwood and William David Cheesman,

Milwaukee, Wis, assignors to Union Carbide Corporation, a corporation of New York No Drawing. Filed Nov. 29, 1963, Ser. No. 327 ,065 4 Claims. (Cl. 14828) This application is a continuation-in-part of our application Serial No. 211,107, filed July 19, 1962, now abandoned, for Metal Quenching Medium.

This invention relates to an improved metal quenching medium and, more particularly, to a novel liquid solution for quenching heat-treated metal to improve the physical properties of the metal.

Ferrous and other metals are ordinarily heat-treated to increase their strength and structural integrity by heating the same to a high temperature and then subjecting the red hot metal to a comparatively cool quenching bath. Conventional quenching baths employed for this purpose consist either of an aqueous solution, which operates at a very high rate but which is unsatisfactory for the reason that internal distortion and cracking of the metal frequently results, or an oil bath is used, wherein distortion is reduced but wherein the slow quenching rate is economically inefficient. Moreover, with conventional oiltype quenching mediums, the metal does not attain the degree of hardness and strength that is preferred for most uses.

With the above considerations in mind, the principal objects of the present invention are to provide a novel metal quenching medium which operates at a high rate and thus requires a relatively short quench cycle time, which results in a minimum of internal stress and distortion in the metal, which imparts uniform hardenability to the metal, and which is otherwise greatly superior to the quenching materials in present use, as will be hereinafter seen.

A more specific object of the present invention is to provide a novel metal quenching medium comprising water and a predetermined volume of polyalkylene glycol, the latter component being adapted to form a layer or coating that completely and continuously wets the metal surface, and through which layer the improved heat conduction characterizing the present quenching process occurs.

A further specific object of the present invention is to provide a novel metal quenching solution including water and polyalkylene glycol, as described, wherein the latter component is completely miscible at aqueous temperatures below 175 F., and wherein said component will not decompose and will remain relatively stable at surface temperatures as highly as 500 F.

A further object is to provide a quenching medium for heated metals which forms a heat-conducting layer that completely and continuously wets the metal surface, as described, which layer can be consistently and accurately reproduced for subsequent applications by maintaining the composition and temperature of said medium stable.

A further object is to provide a quenching material which forms a layer on the surface of the metal as described, which layer of quenching material may be easily removed from the metal surface after the quenching operation either by rinsing orby re-heating the metal. The layer may also be removed spontaneously when the quenching bath adjacent to the metal piece cools below 175 F., whereby the polyalkylene glycol redisperses in water.

A further object is to provide a quenching medium as described, wherein the residual layer of said medium deposited on the metal will not stain, damage, or corrode 3,226,891; Patented Nov. 30, 1965 the metal surface, and wherein when the layer is removed by re-heating the metal as described, said material is not carbonized and does not leave a film which interferes with the subsequent pickling, blasting, or tumbling of the metal surface, as frequently occurs with conventional quenching mediums.

A still further object of the invention is to provide a novel metal quenching medium which is tolerant of contaminants characterizing most heat-treating processes, thereby eliminating the necessity for the purification of said medium, as is required with presently-used materials.

A further important object of the invention is to provide a novel quenching medium which results in a ductility of the quenched metal comparable with the ductility of metals that are re-heated after quenching in oil, water, brine, or other conventional wetting agents, thus eliminating the need for a time-consuming step in the heat-treating process and greatly promoting the efiiciency and economy of the operation.

Still further objects and advantages of the present in vention will appear from the more detailed description average molecular weight of 12,000 to 14,000. The polyfollowing, it being understood that said description is given by way of illustration and explanation only, and not by way of limitation, since it is appreciated that various changes or modifications may occur to those skilled in the art without departing from the scope and spirit of the invention.

In essence, the novel metal quenching medium comprising the present invention consists of a solution containing water and a predetermined volume of polyalkylene glycol and derivatives. It has been found that the polyalkylene glycol component of said solution has the unique characteristic of decreasing in solubility as the temperature of the solution is increased, as when red hot metal is introduced therein. It is applicants belief that due to this novel characteristic of the polyalkylene glycol, said material forms a covering layer over the entire metal surface to the exclusion of the water component of the solution, with the result that no vapor blanket can form at the interface. With conventional aqueous, oil, oil emulsion, or other types of heat transfer mediums, either a vapor blanket or a coating of decomposition products form at the interface during the quenching operation, which products are undesirable for the reason that they act as an insulator and function to retard the heat conduction operation. The polyalkylene interface layer characterizing the use of the present solution, on the other hand, has been found to be an excellent heat conducting medium, and the quench.- ing time cycle is substantially reduced, as will be herein-J after seen.

The water-soluble polyalkylene glycols suitable for the practiceof the invention are known compounds and are viscous liquids even in the high molecular weight range up to those represented by a viscosity of 90,000 Saybolt seconds at F. and higher, which corresponds to an oxyethylene glycols are not compounds of this type since it is known that the members of this series are solids at molecular weights of 600 and upwards. For example, polyoxyethylene glycol having a molecular weight of 600 melts in the range of 20 to 25 C., and a polyoxyethylene glycol having an average molecular weight of about 6000 is a hard wax melting in the range of 60 to 63 C. Very high molecular weight polymers of ethylene oxide are also known which are resinous solids, having a limited practical solubility in water at about 1 to 5 percent concentration where very viscous solutions having viscosities in the range of 500 to 8000 centipoises at 25 C. are obtained depending on the molecular weight which may range from 100,000 to 1,000,000.

In general, the polyalkylene glycols of this invention will'contain both oxyethylene groups and higher oxyalkylene groups, such as oxybutylene and oxypropylene groups, in the molecule and will have average molecular weights from 600 up to 40,000 and higher. The amount of oxyethylene groups in the molecule is such that the polyalkylene glycols are soluble in water at ordinary temperatures and the amount of the oxypropylene or higher oxyalkylene group is such that the polyalkylene glycols remain liquid at ordinary temperatures up to molecular Weights of 40,000 and higher. This ratio may vary, for instance, from an oxyethylene-oxypropylene ratio by weight from about 50-50 to about 90-10. These polyalkylene glycols may be made in a known manner by reacting a mixture of ethylene oxide and propylene oxide or higher alkylene oxide in the weight ratio of from about 50-50 to 90-10 with a compound having at least one active hydrogen atom and up to as many as six such active hydrogen atoms. Suitable compounds are water; monohydric alcohols, such as methanol and butanol; dihydric alcohols, such as ethylene glycol; trihydric alcohols, such as glycerine and trimethylolpropane; tetrahydric alcohols, such as pentaerythritol; and hexahydric alcohols, such as sorbitol; and mono-polyfunctional amines, such as butylamine and ethylene diamine. The products of such reaction, i.e., oxyalkylene polymers, will have linear or branched oxyethylene-oxypropylene chains, depending on the number of reactive sites in the starting compound, and such chains will terminate with hydroxyl groups. Some, or all, of these hydroxyl groups may be etherified by reaction With a dialkyl sulfate, such as diethyl sulfate.

It is to be understood that applicants understanding and explanation of the chemical processes and reactions occurring during the use of their quenching medium is theoretical, and is perhaps inaccurate or incomplete. The desired results are nonetheless obtained with the use of the present invention, and it is the quenching medium per se which is intended to be covered herein.

The exact proportions of polyalkylene glycol and water employed in the novel solution comprising the present invention is dependent upon the particular quenching operation and can be varied within a wide range to obtain the preferred results, as will be seen in the examples included hereinafter. Generally, the best results are provided by a solution comprising water and from 0.1 percent to 30 percent polyalkylene glycol and from 99.9 percent to 45 percent water, suitable percentages of other materials being added to modify the corrosion protection properties of the medium, or to obtain other desired metal characteristics. In the latter respect, it has been found that additives such as nitrites, glucomates, phosphates, silicate-s, borates, hydroxides of metals, and similar materials may be employed without effecting the functional properties of the present invention, and particularly good results have been obtained by adding sodium nitrite and sodium metaborate for corrosion protection. As metioned, with the novel quenching solution comprising the invention, the polyalkylene glycol component is completely miscible with the solution at temperatures below 175 F., and during the quenching operation said component remains stable and will not decompose at interface temperatures as high at 500 F., thus providing a quenching medium which can be advantageously utilized in a wide range of heat-treating operations, and which medium has a long life.

In the following examples and tables the aboveenumerated uses and advantages of the quenching medium comprising the present invention are substantiated, and still further uses and beneficial effects of the invention are also demonstrated, all of which are intended to come within the scope of the invention. While the cited examples pertain to the quenching of steels and cast irons, it is to be understood that the use of the improved medium is by no means limited to ferrous metals, and can be utilized in the treatment of aluminum and other metals or alloys as well.

4 Example 1 In this test, a quenching bath was employed containing 2 parts of polyalkylene glycol A (a polyglycol containing 75 percent oxyethylene groups and 25 percent oxypropylene groups by Weight and having a viscosity of 90,000 Saybolt seconds at F.) and 98 parts water at 70 F. The metal treated consisted of steel bars and tubes which Were quenched from about 1500 F. With respect to the temperature of the heated metal, it is to be understood, of course, that the same be above the critical or austenite start temperatures of the various ferrous metals for best results, and all of the tests were conducted on this basis. Hardenability of the metal was determined by the Rockwell C scale, and the results are shown in the following table:

Rc after draw Material Initial Draw Toughhard., Re temp., ness F. Surface Core G-1040 50-55 700 30-34 30-34 Good. G-1213 Garb .1 62-65 350 55-58 C-1117 Garb 61-64 350 58-60 35-45 Do. G-1018 Garb 58-61 350 56-60 25-28 D0. C-1117 Garb 60-64 350 57-60 22-25 Do. (3-1117 Garb 58-62 350 56-58 D0.

Example 2 A mixture of 4.5 parts polyalkylene glycol A and 95.5 parts water at F. was used as a quenching spray for steel tubes heated to 1600 F. Hardenability was determined by Brinell tests.

A mixture of 3 parts polyalkylene glycol A and 97 parts water at 80 F., employed as immersion bath. The metal tested consisted of 5-inch solid steel rods of inch and /1 inch diameter, 1550 F. and hardness was determined by Rockwell C test.

Materlal Initial Draw Re after Ductility hard., Re temp., F. draw G-1038 53-55 700 38-42 30-40 bend. G-1038 53-55 700 38-42 D0.

Example 4 A mixture of 2.5 parts polyalkylene glycol A and 97.5 parts water at 80 F., heat transfer by immersion. The metal consisted of a flat steel bar, 5 inches x 1% inches x inch, 1550 F., and hardness was determined by Brinell tests.

Material C-1405.

Initial hardness, B.H.N 451-555.

Draw t emp., F 700.

B.H.N. after draw 363-388.

Ductility 30-40 bend.

Example 5 A mixture of 2.8 parts polyakylene glycol A and 97.2

parts water at 80 F., heat transfer by immersion. The metal consisted of a flat steel bar 6 inches x 1% inches x 2 inches with inch diameter holes on 4 inch centers symmetrical to width and length, said bar being quenched from 1550 F.

Material (3-1040. Initial hardness, B.H.N 477-555. Draw temp., F. 700. Draw hardness, B.H.N. 321-363. Ductility 30 bend.

An examination of the holes after drawing disclosed no variance in size of inch holes, while 4 inch center dimension changed .003 inch. Identical tests were conducted using conventional aqueous and oil quenching mediums. A hardness of over 302 B.H.N. could not be obtained using oil, while the use of water caused distortion and cracking.

Example 6 A mixture of 17 parts polyalkylene glycol A and 83 parts water at 80 F., means of heat transfer by immersion. Thirteen individual tests were run on plain malleable cast-iron bars which were held at 1500 F. for 2 hours, quenched and drawn at 700 F. for 2 hours.

Test No. Propon Ultimate Elongation Hardness,

tional limit strength percent B .H.N.

p.s.i. p.s.i.

Average 80, 000 101, 000 3 266 1 Out of gauge.

The results of this test established conclusively that quality pearlitic malleable iron can be manufactured from plain malleable iron by simple processing utilizing the novel quenching medium comprising the present invention.

Example 7 A mixture of 19 parts of polyalkylene glycol A and 81 parts water at 80 F., heat transfer by immersion. The test was performed on 500 manufactured parts to determine if white iron parts could be processed to an increased hardness without damages. The result was that none of the parts was cracked, and increased hardness was obtained.

Initial hardness, B.H.N. 444-461. Draw temp., F. 400. B.H.N, after draw 444. Remarks No cracks cross section hardness 418-429 B.H.N.

Example 8 A mixture of 18 parts of polyalkylene glycol A and 82 parts Water at 80 F., heat transfer by immersion. This test was performed on 2000 manufactured malleable iron parts to determine the effect of increasing the initial, or austenizing, temperature of the metal on the ultimate physical properties of the metal when using the present quenching medium.

Initial Draw B.H.N. Austenizlng Temp., hardness, temp., after draw Ductility F. B.H.N. F.

269, 285 900 241-255 20 Bend. 269,285 900 241-255 Do. 269-285 900 241-255 Do. 269-285 900 241-255 Do.

The above results show that metallurgical structure resulting from the use of the quenching medium comprising the present invention is not influenced by increased austenizing temperatures, thus permitting the use of a higher input heat zone and a shorter in and out heat cycle than is possible with conventional quenching materials.

Example 9 A mixture of 19 parts of polyalkylene glycol A and 81 parts water, heat transfer by immersion. This experiment was performed on 4000 manufactured malleable parts to determine the influence of different quenching medium temperatures on the composition and structural integrity of the tested parts.

Draw. B.H.N. Poly- Initial Hardness, temp., after alkylene Ductility,

B.H.N. I. draw temp., F.

269-285 900 241-255 76 20 Bend 900 241-255 81 D0. 900 241-255 82 Do. 900 241-255 116 D0. 900 241-255 135 D0.

Results of this experiment demonstrated that the hardness developed by quenching in the present medium is not influenced by variations in the medium temperature of the quenchant within the indicated range.

Example 10 A mixture of 18.5 parts polyalkylene glycol A and 81.5 parts water, heat transfer by immersion. The metal employed in this experiment consisted of .505 inch test bar specimens representing melting heats of malleable iron over a three months period. The processing consisted of heating to 1500 F. for two hours followed by quenching in the above mixture at the indicated medium temperatures.

Temperature, Initial Date F. of hardness, Ductility Quench .H.

March 14 83 269 18 bend. 82 255 17 bend. 86 269 20 bend. 83 255 22 bend. 86 255 25 bend. 86 255 16 bend. 82 255 19 bend. 84 255 20 bend. 85 255 D0. 84 255 15 bend. 80 255 20 bend. 74 262 17 bend. 79 255 16 bend. 82 269 20 bend. 75 255 18 bend. 73 269 17 bend. 84 255 21 bend. 78 285 15 bend. 82 255 20 bend. 79 241 21 bend. 255 25 bend. 63 269 24 bend. 65 255 20 bend. 67 269 17 bend. 64 255 19 bend. 255 21 bend. 86 255 20 bend. 76 255 17 bend. 76 255 25 bend. 75 255 22 bend. 63 255 21 bend.

This experiment illustrates that the effectiveness of the present quenching medium in producing uniform physical properties from various heats of malleable iron, and the ability of the medium to maintain its stability without additions over extended period of service.

It will be seen from the foregoing experiments that the novel and improved quenching medium comprising the' present invention may be advantageously employed for varying heat-treating operations, and that the relative percentages of polyalkylene glycol and water in the solution, as well as additional corrosion-resistant ingredients or the like, can be varied substantially to suit particular quenching requirements.

A principal advantage of the present invention, of course, is that its use results in less internal stresses and dimensional distortion, cracking, or warping of the metal than occurs when conventional cooling agents are used, and particularly aqueous mediums. Moreover, the use of the present invention results in greater and more uniform hardenability than is obtained with conventional oiltype mediums, and requires a shorter quench cycle time (about one-third the time). With respect to the timesaving feature inherent in the present invention, it has been found that with the present medium the ductility of the quenched metal is comparable to the ductility of metals that are tediously re-heated after quenching in oil or other conventional materials (see Example 3), thus substantially reducing the time requirement and promoting more economical heat treating.

In the use of the novel quenching medium hereinab ove described, the polyalkylene glycol component included therein has the unique characteristic of decreasing in solubility as the temperature of the solution is increased, as when red hot metal is introduced therein. Consequently, said component forms a covering layer over the metal which continuously wets the same, and which functions as the heat-conducting agent, as described. After the completion of the quenching process, the transparent, residual layer of polyalkylene glycol material will redi-s-solve in the quenching bath on cooling or it can be removed byrinsing with water or by re-heating the metal to vaporize said material. In the event the layer is removed by rinsing, it can be easily recovered for further use by reclaiming the rinse water. When the residual material is removed by re-heating the metal, to vaporize the same, such re-heating does not carbonize or decompose the polyalkylene glycol and no film is left on the metal which would interfere with normal pickling, blasting, or tumbling, ordinarily used to prepare the metal surface for finishing. Moreover, such vapors do not condense to a degree necessitating venting or exhausting of the work area.

Additional advantages of the novel quenching medium comprising the present invention are that the mediumis stable and will not decompose even at relatively high temperatures, the solution is non-inflammable and does not create a fire hazard, it is free from odors, it is not irritating to human skin, and it will not damage or corrode the metal, as mentioned. Further, the present medium is compatible with regular storage, circulating, pumping and transferring equipment;- there is no necessity for waste disposal, such as caustic wastes and petroleum or fatty oil wastes; the medium is compatible with conventional filtering processes; and it is susceptible to accurate temperature control.

It is to be understood, of course, that the present invention is intended to include not only the particular percentages and rangesof the components hereinabove recited, but also any and all variations or changes therein as may comewithin the spirit of the invention and within the scope of the following claims.

What is claimed is:

1. A method for quenching heated metal which comprises contacting said heated metal with a liquid quenching medium consisting principally of'water having dissolved therein a. liquid water-soluble oxyalkylene polymer, said oxyalkylene polymer being characterized by the pres ence of both oxyethylene groups and higher oxyalkylene groups.

2. A method for quenching heated metal which comprises contacting said heated metal with a liquid quenching medium consisting principally of water having dissolved therein a liquid Water-soluble oxyalkylene polymer, said oxyalkylene polymer being characterized by the pres: ence of both oxyethylene groups and oxypropylene groups, transferring heat from the heated metal to the quenching medium and causing a layer of said oxyalkylene polymer to wet the surface of said metal, and withdrawing the quenched metal from the quenching medium.

3. Method as claimed in claim 1 in which the quenching medium contains from about 45 percent to 99.9 percent by weight of water and from about percent to 0.1 percent by weight of oxyalkylene polymer.

4. Method as claimed in claim 1 in which the quenching medium is at a temperature between 0 F. and 220 F.

References Cited by the Examiner UNITED STATES PATENTS 2,770,564 11/1956 Gordon 148-30 3,022,205 2/1962 Chase et al. 148-28 DAVID L. RECK, Primary Examiner.

WINSTON A. DOUGLAS, Examiner.

Disclaimer 3,220,893.R0bert R088 Blackwood and William David Okeesman, Milwaukee,

Wis. METAL QUENCHING MEDIUM. Patent dated N 0v. 30, 1965.

Disclaimer filed Jan. 10, 1980, by the assignee, Union Carbide Uorpomtion.

Hereby enters this disclaimer to the remaining term of said patent.

[Ofiicz'al Gazette, March 18,1980.] 

1. A METHOD FOR QUENCHING HEATED METAL WHICH COMPRISES CONTACTING SAID HEATED METAL WITH A LIQUID QUENCHING MEDIUM CONSISTING PRINCIPALLY OF WATER HAVING DISSOVLED THEREIN A LIQUID WATER-SOLUBLE OXYALKYLENE POLYMER, SAID OXYALKYLENE POLYMER BEING CHARACTERIZED BY THE PRESENCE OF BOTH OXYETHYLENE GROUPS AND HIGHER OXYALKYLENE GROUPS. 